Most viral vectors used for gene editing allow efficient high transduction without specificity for certain cell types. The lenti- or retro-viral vectors are often pseudotyped with gylcoproteins of viruses with a broad cellular tropism allowing gene transfer into a variety of cell types. This procedure is sufficient for ex vivo manipulation as for example in generating Chimeric antigen receptors (CAR) T cells, which have shown significant clinical benefits to patients with B-cell malignancies. However, production of CAR T cells requires extensive and time-consuming procedures of cell isolation, sorting, transduction and in vitro expansion of T cells. Our group has developed a variety of viral vectors for targeting of individual cell types. By delivering the CAR gene directly in vivo into the patients’ T-cells with lentiviral vectors specific for CD8+ or CD4+ T-cells we aim at circumventing the expensive ex vivo production. Our targeted lentiviral vector (CD8-LV or CD4-LV) already proofed to selectively transduce CD8+ or CD4+ T-cells with no signs for off target transduction, in vitro and in several mouse models in vivo. In vivo generated CAR T cells were functional and controlled tumor growth.

Recently a novel insertion site within a loop region of the AAV capsid allowed the insertion of nanobodies (Eichhoff et al. 2019). We generated DARPins Targeting AAVs (DARTs) with a Designed Ankyrin Repeat Proteins (DARPin) inserted into the Loop of AAV capsids. These allow for a rational targeting of AAVs to certain cells types with almost the same genome copies as recombinant AAVs. AAVs have a much better safety profile, which allows for in vivo applications and they can be produced at high titers. Different AAV based vectors are already in clinical trial and three products are already aproved in Europe and US. Therefore DART-AAV seem to be a highly interesting approach for in vivo gentherapy approaches.